When you clear the recent documents list, the window containing the recent documents is redrawn to only contain "No items found" and "clear". However if the previous window which was drawn bigger then it will become detached from the places menu and float on its own which looks quite odd.
I can't say I have seen this problem. Have you tried a different window manager? Turning off any fancy 3d effects? A different graphics driver? Can you take a screenshot? Have you seen this in any other applications? What version are you running? What OS and what version of that?
Created attachment 1523 Before the bug This is before the bug.
Created attachment 1524 After the bug This is after the bug. Notice the big gap between the floating menu with "No items found" and the places menu
I've created a couple of attachments to demonstrate the bug. It's xfwm4 4.4.2 with no 3D or compositing or anything fancy going on at all. I run Debian unstable so GTK is 2.12.7
Ah, I didn't realize you meant bigger in width. Regardless, I still don't have that problem on Debian testing. I'll look into it some more when I get the time, or replace that menu with a home-brewed one that can support right-clicking as well.
I was able to reproduce the problem by moving the plugin near the right edge of the screen, thus forcing the Recent Documents submenu to pop up to the left.
This little hack gives it more reasonable behavior. http://svn.xfce.org/index.cgi/xfce-goodies/revision/?rev=4522
OK, I now have it repositioning the menu any time the GtkRecentManager emits the "changed" signal. I suspect it should behave pretty well now. Please test with trunk.